Function apply_basic_mode_session_llm_overrides 

pub fn apply_basic_mode_session_llm_overrides(
    base_config: &AppConfig,
    session: &AgentSession,
) -> (AppConfig, EffectiveLlmConfig)

Apply session-scoped LLM overrides (for basic/non-TUI CLI mode) and return a cloned config together with the effective provider/model.

This resolves the override from the session, clones base_config, applies the override via apply_cli_session_llm_overrides, and returns both.